Add configuration flag to allow running the tests with valgrind

### Describe the request

As pointed out by @tttapa over [here](https://github.com/arduino/ArduinoCore-API/pull/193#issuecomment-1666995795) we can not enable address sanitizers since `valgrind` in `CMakeLists.txt` would refuse to run it. Consequently it would be desirable to have a configuration flag that would allow to disable using valgrind for running the tests.

### Describe the current behavior

`arduino/cpp-test-action` always uses `valgrind` when running the unit tests, though there are situations where this may be not sensible to do.

### 'arduino/cpp-test-action' version

main

### Additional context

_No response_

### Issue checklist

- [X] I searched for previous requests in [the issue tracker](https://github.com/arduino/cpp-test-action/issues?q=)
- [X] I verified the feature was still missing when using the latest version
- [X] My request contains all necessary details

Start with CMakeLists.txt and the cpp-test-action test-running entry point to trace where valgrind is always invoked. Add a configuration flag that skips valgrind while preserving unit-test execution, then verify the default behavior and the disabled-valgrind path.

Written by the indexing model from the issue text.